it truly depends on what kind of quilt s you make---if you never make anything with peices smaller than 5" squares---then anything smaller would be ...just storing...if you are an appliquer & use itty bitty pieces for all kinds of things---then itty bitty peices should be saved...if you like making water color quilts with 2" squares---then 2" would be the ones to save...
so, decide what you will use===then pass on the rest- there is always someone working on a postage stamp quilt (sometimes 1/2" squares) or something and willing to take your scraps you have no use for off your hands- keep the ones you will use- there's not alot of reason to hold onto ones you will never use- that will just take up space-
many people appreciate your leftovers you would never use.